On 17/08/2021 19:09:28+0800, tonywwang-oc@xxxxxxxxxxx wrote: > > > On August 16, 2021 8:36:48 PM GMT+08:00, Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> wrote: > >On 16/08/2021 18:03:13+0800, Tony W Wang-oc wrote: > >> > >> On 16/08/2021 16:24, Alexandre Belloni wrote: > >> > Hello, > >> > > >> > On 16/08/2021 21:47:18+0800, Tony W Wang-oc wrote: > >> >> When the RTC divider is changed from reset to an operating time > >base, > >> >> the first update cycle should be 500ms later. But on some Zhaoxin > >SOCs, > >> >> this first update cycle is one second later. > >> >> > >> >> So set RTC time on these Zhaoxin SOCs will causing 500ms delay. > >> >> > >> > > >> > Can you explain what is the relationship between writing the > >divider and > >> > the 500ms delay? > >> >> Isn't the issue that you are using systohc and set_offset_nsec is > >set to > >> > NSEC_PER_SEC / 2 ? > >> > > >> No. > >> When using #hwclock -s to set RTC time and set_offset_nsec is > >> NSEC_PER_SEC / 2, the function mc146818_set_time() requires the first > >> update cycle after RTC divider be changed from reset to an operating > >> mode is 500ms as the MC146818A spec specified. But on some Zhaoxin > >SOCs, > >> the first update cycle of RTC is one second later after RTC divider > >be > >> changed from reset to an operating mode. So the first update cycle > >after > >> RTC divider be changed from reset to an operation mode on These SOCs > >> will causing 500ms delay with current mc146818_set_time() > >implementation. > >> > > > >What happens with hwclock --delay=0 -s ? > > With "hwclock --delay=0 -s" still have this problem. Actually, this 500ms delay caused by writing the RTC time on these Zhaoxin SOCs. > As I've tested, with hwclock --delay=0 -w can fix it too. > Both -s and -w end up calling set_hardware_clock_exact() so both should end up with the correct time. If this is not the case, then hwclock needs to be fixed. -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
